This invention relates to a rate converting device for converting an input data signal having an input transmission rate into an output data signal having an output transmission rate.
In general, a rate converting device is for use in a communication system comprising first and second communication circuits which are connected to each other through a communication path having a path transmission rate. The communication system may be, for example, a digital radio communication system. The communication path may be, for example, a radio channel.
When the first communication circuit communicates with the second communication circuit through the communication path, the first communication circuit is supplied with an input data signal having an internal transmission rate different from the path transmission rate. Inasmuch as the internal transmission rate is different from the path transmission rate, the first communication circuit comprises the rate converting device for converting the input data signal having the internal transmission rate into an output data signal having the path transmission rate. The output data signal is modulated into a first transmission signal which is transmitted to the second communication circuit through the communication path.
On the other hand, the first communication circuit may receive a second transmission signal having the path transmission rate from the second communication circuit. The first communication circuit demodulates the second transmission signal into a demodulated signal having the path transmission rate. The rate converting device is operable to convert the demodulated signal into a converted signal having the internal transmission rate. Similarly, the second communication circuit comprises the rate converting device.
A conventional rate converting device is disclosed in Japanese Unexamined Publication Tokkai Hei 1-42958 (42958/1989). The conventional rate converting device comprises a transmission rate converting section and a reception rate converting section. The transmission rate converting section is operable to convert the input data signal having the internal transmission rate into the output data signal having the path transmission rate. The reception rate converting section is operable to convert the demodulated signal having the path transmission rate into the converted signal having the internal transmission rate.
Now, it will be assumed that the internal transmission rate is represented by f1 and the path transmission rate is represented by f2. A relationship between the internal transmission rate and the path transmission rate is given by: EQU f2=(m/n)f1,
where m and n are first and second natural numbers, respectively. The first natural number m is greater than the second natural number n.
It will be assumed that the output data signal has an output frame of a frame length L. Inasmuch as the frame length L must generally be not shorter than the first natural number m, it is to be noted that the frame length L becomes long in order to make the path transmission rate high. Namely, it is to be noted that the path transmission rate is defined by the frame length L. As a result, it is difficult to set the path transmission rate as desired independent of the frame length in the conventional rate converting device.